Fuel injectors typically include a valve needle which is actuated to open and close an injector port to regulate fuel to the engine. In many injectors, the valve needle is electromagnetically actuated by a coil assembly that induces a magnetic flux in an armature connected to the valve needle. The armature is attached to one end of the valve needle, while the opposing end of the needle is shaped to seal against the valve seat for opening and closing the injector port.
Misalignment between the valve needle and the valve seat is a major cause of excessive injector leakage. To ensure acceptable alignment, an upper guide and a lower guide are typically employed to maintain the needle-armature assembly in a position perpendicular and concentric to the valve seat sealing surface. More specifically, this requires good concentricity between the armature and needle guiding faces, good concentricity between the upper and lower guide faces, and sufficiently tight upper and lower guide clearances.
Failure to meet these concentricity requirements can cause many problems, including the needle tilting from the axis, the needle binding to the guides, the needle being bent by the guides, the needle wearing on the guiding faces, and in the worse scenario, a gap being formed in the circumferential sealing surface between the tip of the needle and the valve seat. Therefore, needle misalignment deteriorates the injector performance by increasing needle-guide friction, accelerating wear of needle and guides, and causing leakage. On the upper end of the armature-needle assembly, the needle misalignment results in uneven air gap between the two magnetic pole faces of the armature. This may cause non-uniform magnetic flux distribution, inconsistent stroke, and bad flow linearity.
It can therefore be seen that the formation of the upper and lower guides, as well as of the needle-armature assembly is of paramount importance. Typically, the upper and lower guides are small parts which are individually formed and attached to other structures forming the fuel injector valve. The separate guides usually have a complicated shape with a central guiding hole and several flow passing holes. This requires precision grinding on both the outer diameter and the inner diameter surfaces, as well as very tight tolerances to maintain the concentricity. Unfortunately, these guide pieces are usually hardened and are too small to be held appropriately for machining. Furthermore, the assembly and fastening method for these guides in the injector are complicated, and may introduce additional problems. All of the above also increases cost. Therefore, there exists a need to provide a fuel injector having lower and/or upper guides which improve overall performance by maintaining good concentricity between the guiding faces, the valve assembly and the valve seat, while providing simple and cost effective manufacture and assembly.
While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.